This invention relates to the production of organic carboxylic acid esters and in particular to a process for simultaneously coproducing ethyl acetate and isopropyl acetate in a reaction mixture comprising a mixed alcohol stream of ethanol and isopropanol, with acetic acid, in the liquid phase in the presence of an acidic catalyst. The invention further relates to the subsequent separation of ethyl acetate and isopropyl acetate from the crude acetate ester mixture, and to the removal of impurities which may be present.
It is well known to produce esters such as ethyl acetate or isopropyl acetate by reaction of an ethanol or isopropanol respectively with acetic acid in the presence of an acidic catalyst. However, in the coproduction of esters, difficulty is encountered in driving the esterification reactions to completion, especially with mixtures of alcohols with dissimilar reactivity, thereby resulting in acetate product contaminated with unreacted alcohols. It is also known to coproduce these esters in a single reactor by operating the reactor sequentially, i.e., by first producing one ester by reaction of the acid with the first alcohol, and then in a swing operation changing over to a second alcohol to produce the second ester. In all of these reactions involving the use of a mixture of alcohols for esterification, it is important to use relatively pure reactants for reaction with acetic acid. This is especially important if the esters are coproduced in a process for the simultaneous rather than the sequential production of both esters. The use of reactants of high purity may not be economic commercially for it would add significantly to the cost of producing both esters. It has been relatively difficult to coproduce simultaneously a mixture of these esters from a relatively impure set of reactants, primarily because if the alcohol is contaminated with impurities, for example, xe2x80x9cheavyxe2x80x9d or C3 or greater alcohols, it is difficult to separate the eventual ester product from the impurities.
WO 98/42652 (BP Chem.) describes ester coproduction for the coproduction of ethyl acetate and n-butyl acetate. The reference describes use of impure crude industrial ethanol and xe2x80x9coxoxe2x80x9d based n-butanol in a liquid phase esterification reaction system. The process is capable of using relatively impure reactants and provides for removing some of the aldehyde type impurities of the alcohols by the use of resin guard beds.
WO 98/25876 (Sasol Chem.) describes production of organic carboxylic acid esters employing Fischer Tropsch derived alcohols or carboxylic acids, said esterfication reaction occurring in the vapor phase. Among other esters, WO""876 exemplifies the production of ethyl acetate and/or butyl acetate. It is stated that due to the complexity of Fischer Tropsch product streams, it is normally uneconomic to purify the alcohols obtained to a purity in excess of 99%. WO ""876 describes use of the Fischer Tropsch alcohol without purification prior to use. The alcohol, or Fischer Tropsch carboxylic acid, if used, is employed as is and blended with acetic acid in the reaction system.
The present invention is directed to a process for the simultaneous coproduction of ethyl acetate and isopropyl acetate, comprising reacting an alcohol mixture of ethanol and isopropanol with acetic acid, in the liquid phase, in the presence of an acidic catalyst wherein the reaction is carried out at elevated temperature and at a pressure sufficient to effect esterification of the reactant. An example of an alcohol mixture is that which is derived from the purification of a Fischer Tropsch alcohol mixture. Fischer Tropsch alcohol mixtures contain impurities. In the present invention, impurities of primary concern are the heavy components, or the C3 or C4 alcohol components of the Fischer Tropsch mixture. The Fischer Tropsch mixture may or may not be purified, prior to use. Purification of the Fischer Tropsch mixture can occur employing distillation or alternatively employing extractive distillation with water. If the Fischer Tropsch mixture is used without prior purification, high boiling ester byproducts are produced during the esterification reaction and removed from the reaction product during the purification process of the respective ethyl and isopropyl acetate products. The crude mixed ester product is separated into purified ethyl and isopropyl acetate products via a series of distillation towers.
Examples of percent alcohol mixtures to employ include alcohol mixtures containing between about 90% ethanol:10% isopropanol to between about 10% ethanol:90% isopropanol, or alternatively the mixture is between about 80% ethanol:20% isopropanol to between about 60% ethanol:40% isopropanol.
Employing the current process, both ethyl acetate and isopropyl acetate are recovered at greater than about 99.5% purity and up to or greater than about 99.7%. Presently the industry accepts specification grade ethyl acetate and specification grade isopropyl acetate as being a minimum purity of 99.5%.